1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a scanning method in a wireless local area network (WLAN).
2. Related Art
With the recent development of information communication technology, a variety of wireless communication techniques are being developed. From among them, a WLAN is technology for wirelessly accessing the Internet at homes or companies or in specific service providing areas by using portable terminals, such as a Personal Digital Assistant (PDA), a laptop computer, and a Portable Multimedia Player (PMP), based on radio frequency technology.
Communication in a WLAN according to the IEEE 802.11 standard is premised on that communication is made within an area known as a basic service set (BSS). A BSS area may change according to propagation characteristics of a wireless medium, so a boundary thereof is somewhat indefinite. A BSS may be basically classified into an independent BSS (IBSS) and an infrastructure BSS. The IBSS refers to a BSS forming a self-contained network in which an access to a distribution system (DS) is not permitted, and the infrastructure BSS refers to a BSS including one or more access points (APs), a distribution system, and the like, in which an AP is used in every communication process including communication between stations (STAs).
When a STA wants to access a wireless network, the STA may use two scanning methods including passive scanning and active scanning to discover an accessible wireless network (e.g., a BSS, an IBSS, etc.), namely, an AP to which the STA is to be connected.
A passive scanning method uses a beacon frame transmitted from an AP (or an STA). Namely, when an STA wants to access a wireless network, the STA receives a beacon frame periodically transmitted from an AP, or the like, that manages the corresponding wireless network (e.g., a BSS, an IBSS, etc.) to discover an accessible wireless network (e.g., a BSS, an IBSS, etc.). In the case of passive scanning, the STA should wait until when a beacon frame is transmitted from the AP, so much time may be taken for the STA to discover the AP. In general, a transmission period of a beacon frame is 100 ms.
According to an active scanning method, an STA, which wants to access a wireless network, first transmits a probe request frame and an AP (or an STA), which has received the probe request frame, responds thereto by a probe response frame. Here, every AP, which has received the probe request frame, responds by a probe response frame, flooding of probe response frames occurs. Also, since the STA sequentially scans every channel of a wireless medium, a scanning time may be lengthened.
Thus, a scanning method for reducing flooding of probe response frames and shortening time required for performing scanning is required.